Also it's probably true that Spike became a monster because of Angelus, Dru and Darla. They taught him stuff for sure,and we saw in "Destiny" that William was eager to please his new family.

I disagree. William became a monster, because Dru turned him into a vampire, yes. But the rest was up to him.

Darla, Dru and Angelus' desire to teach would have meant nothing without Spike's desire to learn. He didn't have to do that. He didn't have to try to please them. He didn't have to stick around. And he's certainly not under their control - In FFL, it's pretty clear that he does what he pleases. It is Angelus and Darla who is forced to stop being what they want to be, in order to still have William and Drusilla with them. Living in the squalid mineshafts instead of the splendor that Angelus and Darla prefer.

But Angelus wants to have a family, and so he must make compromises.

Spike is not a patsy. He genuinely likes doing what he does. There's nothing fake about his riot-induced exhilaration. In one minute or another, sure, Spike would do things to 'stick it to Angelus' but more than that, he does what he does because he enjoys it.

And his idea of fun came to him long before he ever knew who Drusilla was. He just didn't have the drive or opportunity to act upon it.